This invention relates to propellants and more particularly to rubber-based propellants.
Rubber-based propellants must be flexible and strong enough to withstand tremendous pressures and shocks which occur when the propellant is ignited. Otherwise, the propellant will crack and break and thus burn improperly. Unfortunately, rubber-based propellants become less flexible and less strong as they age. It is important, therefore, to find rubber-based propellant composite which resist the aging process.
An important aspect of the search is the testing of the aging properties of various rubber-based propellant composites. Simply exposing the propellants to normal environmental conditions is impractical because of the length of time such testing takes. One prior art approach is to expose the propellants to high temperatures (e.g. 140.degree. F.-165.degree. F.). The data from such test provide only a vague indication of the aging properties of the tested propellants. This is due in part to reactions between propellant ingredients which occur at elevated temperatures but do not occur at ambient storage temperatures.
The influence of ozone on the rate of cracking of strained rubber samples has been studied (see, for example, Newton, R.G.; "Mechanism of Exposure-Cracking of Rubbers," Journal of Rubber Research, volume 14, No. 4 (April 1945), pp 39-63.) These prior art tests focus on the study and characterization of cracks which appear in the rubber sample. This data is of little value in evaluating the useful life of rubber-based propellants. Well before cracks appear the rubber-based propellants usually have lost the minimum strength and flexibility which they need for proper ignition and burning.